How does the QRS morphology differ in junctional rhythms compared to normal sinus rhythms?

In junctional rhythms, the QRS complexes can indeed appear normal in shape but are characterized by the absence of preceding P waves. This absence occurs because the atrial depolarization (which generates the P wave) is not initiated from the sinoatrial node, as is the case in normal sinus rhythms. Instead, the impulse originates from the junctional area of the heart, typically the atrioventricular (AV) node, which may stimulate the ventricles directly without the atrial contraction.

As a result, while the QRS complexes themselves can look normal when measured (indicating that ventricular depolarization occurs in the usual fashion), the lack of P waves differentiates junctional rhythms from normal sinus rhythms, where the P waves would typically precede each QRS complex. This fundamental difference in the relationship between P waves and QRS complexes is crucial for identifying junctional rhythms on an electrocardiogram (ECG).